Advanced graphite additive for enhanced cycle-life of lead-acid batteries

ABSTRACT

An Advanced Graphite, with a lower degree of ordered carbon domains and a surface area greater than ten times that of typical battery grade graphites, is used in negative active material (NAM) of valve-regulated lead-acid (VRLA) type Spiral wound 6V/25 Ah lead-acid batteries. A significant and unexpected cycle life was achieved for the Advanced Graphite mix, where the battery was able to cycle beyond 145,000 cycles above the failure voltage of 9V, in a non-stop, power-assist, cycle-life test. Batteries with Advanced Graphite also showed increased charge acceptance power and discharge power compared to control groups.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 12/984,023 filed Jan. 4, 2011, the disclosure of which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to lead-acid batteries, andmore particularly to an Advanced Graphite additive to enhance the cyclelife of lead-acid batteries, to batteries containing such an additive, apaste for such batteries, and methods for making such batteries.

BACKGROUND

The lead-acid battery is the oldest and most popular type ofrechargeable energy storage device, dating back to the late 1850's wheninitially conceived by Raymond Gaston Plante. Despite having a very lowenergy-to-weight ratio and a low energy-to-volume ratio, the lead-acidbattery can supply high-surge currents, allowing the cells to maintain arelatively large power-to-weight ratio. These features, along with theirlow cost, make lead-acid batteries attractive for use in motor vehicles,which require a high current for starter motors. A lead-acid battery isgenerally composed of a positive electrode and a negative electrode inan electrolyte bath. Typically, the electrodes are isolated by a porousseparator whose primary role is to eliminate all contact between theelectrodes while keeping them within a minimal distance (e.g., a fewmillimeters) of each other. A separator prevents electrodeshort-circuits by containing dendrites (puncture resistance) andreducing the Pb deposits in the bottom of the battery.

A fully charged, positive lead-acid battery electrode is typically leaddioxide (PbO₂). The negative current collector is lead (Pb) metal andelectrolyte is sulfuric acid (H₂SO₄). Sulfuric acid is a strong acidthat typically dissociates into ions prior to being added to thebattery:

H₂SO₄→H⁺+HSO₄ ⁻

As indicated in the following two half-cell reactions, when this celldischarges, lead metal in the negative plate reacts with sulphuric acidto form lead sulphate (PbSO₄), which is then deposited on the surface ofthe negative plate.

Pb(s)+HSO₄ ⁻(aq)→PbSO₄(s)+H⁺(aq)+2e⁻ (negative-plate half reaction)

PbO₂(s)+3H⁺(aq)+HSO₄ ⁻(aq)+2e⁻→PbSO₄(s)+2H₂O (positive-plate halfreaction)

During the discharge operation, acid is consumed and water is produced;during the charge operation, water is consumed and acid is produced.Adding the two discharge half-cell reactions yields the full-celldischarge reaction:

Pb+PbO₂+2H2SO₄→2PbSO₄+2H₂O (full-cell discharge equation)

When the lead-acid battery is under load, an electric field in theelectrolyte causes negative ions (in this case bisulfate) to drifttoward the negative plate. The negative ion is consumed by reacting withthe plate. The reaction also produces a positive ion (proton) thatdrifts away under the influence of the field, leaving two electronsbehind in the plate to be delivered to the terminal.

Upon recharging the battery, PbSO₄ is converted back to Pb by dissolvinglead sulphate crystals (PbSO₄) into the electrolyte. Adding the twocharge half-cell reactions yields the full-cell charge reaction.

PbSO₄(s)+H⁺(aq)+2e⁻→Pb(s)+HSO⁻ (aq) (negative-plate half reaction)

PbSO₄(s)+2H₂O→PbO₂(s)+3H⁺(aq)+HSO₄ ⁻(aq)+2e⁻(positive-plate halfreaction)

PbSO₄(s)+H⁺(aq)+2e⁻→Pb(s)+HSO₄ ⁻(aq) (full-cell charge equation)

When the battery repeatedly cycles between charging and discharging, theefficiency of dissolution of PbSO₄ and conversion to Pb metal decreasesover time. As a result, the amount of PbSO₄ continues to increase on thesurface of negative plate and over time forms an impermeable layer ofPbSO₄, thus restricting access of electrolyte to the electrode.

Over the years, several additives, including expanders, have been usedin an attempt to lessen the growth of lead sulphate and improve batteryperformance. Expanders act as anti-shrinkage agents and are an importantcomponent of lead/acid batteries because they prevent performance lossesin negative plates that would otherwise be caused by passivation andstructural changes in the active material. To make a negative platespongy and prevent the solidification of lead, expanders were developedfrom a mixture of carbon black, lignin derivatives (e.g., lignosulphate,lignosulfonates), and barium sulphate (BaSO₄). These expanders can beincorporated into a battery's negative plates in several ways, includingadding the individual components to a paste mix and adding a pre-blendedformulation.

Carbon black is typically added to the negative active material (NAM) toincrease: (i) electrical conductivity; (ii) surface area of the NAM; and(iii) nucleating PbSO₄ crystals. Carbon black is substantially pureelemental carbon, typically in the form of colloidal particles producedby an incomplete combustion or thermal decomposition of gaseous orliquid hydrocarbons under controlled conditions. It is a black, finelydivided, pellet or powder.

The presence of lignin derivatives (e.g., lignosulphate,lignosulfonates, and other complex aromatic polyethers) helps preventthe formation of an obstructive PbSO₄ layer on the electrode surface andfacilitates the formation of a porous layer built up of individual PbSO₄crystals. Lignin derivatives have the property of being strongantiflocculents (e.g., they prevent colloids from coming out ofsuspension in the form of flocs or flakes) and comprise a largehydrophobic organic part (R⁺) and a small hydrophilic inorganic fraction(SO₃ ⁻). As a result, lignin derivatives are water-soluble. For example:

RS0₃Na→RSO₃ ⁻+Na⁺

The hydrophobic part of the RSO₃ ⁻ anion will be adsorbed on the surfaceof the lead particles, and thus the hydrophilic part of the anion willphase-out to the aqueous electrolyte phase. This results in an increasein the repulsion potential, which prevents the particles from coalescingor sintering. Many different lignosulfonates have been used inexpanders; however, their effects on the performance of lead/acidbatteries varies dramatically based on the expander formula and batterytype application (e.g., Starting, Motive, Standby).

Barium sulfate, being isomorphic to PbSO₄, acts as a nucleation agentand ensures uniform distribution of PbSO₄ crystals throughout the activemass volume. The ability of barium sulfate to act as a site for leadsulfate precipitation is due to the similar structures of the twocompounds. Strontium sulfate has also been shown to be an effectiveexpander. The inert barium sulfate provides a large number of sites forthe precipitation of lead sulfate crystallites and thereby prevents itsdeposition as a thin, impermeable, passivating PbSO₄ film.

A notable difference between expanders used in automotive and industrialapplications is the ratio of barium sulfate to carbon. For example, inautomotive batteries, a high fraction of lignosulfonate (25-40%) may beused, whereas in industrial batteries, a smaller percentage oflignosulfonate may be used (0-10%). The higher percentage oflignosulfonate in automotive plates may be useful in producing highcold-cranking amperes, whereas a larger amount of barium sulfate inindustrial plates may help prevent passivation during deep cycling andprovide greater durability.

Conductive additives in positive plates, such as BaPbO₃ (Bariummetaplumbate); Pb₃O₄ (Red lead), Titanium based compounds (e.g., Ti₄O₇,TiSi₂, TiO₂), and graphite have been used to improve the power densityand corrosion resistance in lead-acid batteries. Similarly, highersurface area additives (e.g., glass microspheres, particulate silica,zeolite, and porous carbons) have also been added to negative paste toimprove electrolyte access and enhance cycle life.

For several decades, carbon has been a popular additive to the NAM inlead-acid batteries. Although the role of carbon in NAM may be generallyunclear, several beneficial effects have been identified. For example,carbon nucleates the PbSO₄ crystals, resulting in smaller crystals thatmay be more easily dissolved into the electrolyte during chargingprocesses. This restricts the progress of plate sulfation (e.g.,formation of a PbSO₄ layer) and increases the useful life of the batteryin high-rate, partial state-of-charge (HRPSoC) duty. High surface-areacarbons can act as a reservoir for electrolyte within NAM, thus reducingthe possibility of plate dry-out.

A combination of highly conductive graphite, high surface area carbonblack and/or activated carbon is often used in NAM. In graphite, theatoms are typically arranged in planar hexagonal networks (e.g.,graphene layers) held together by strong sp² bonds resulting in highin-planar electronic conductivity. A disordered carbon typically ariseswhen a fraction of carbon atoms is sp³ hybridized rather than sp². Theelectronic conductivity of mixed carbon depends on the distribution ofsp³ carbon in sp² domains. Although graphite additives in activematerial decrease the resistivity of the paste by forming a conductivepath around the PbSO₄ crystals, they are reported to have lower surfaceareas (typically in the order of 10-30 m²/g). A second carbon additiveis generally required to increase the total surface area of the NAM toimprove the accessibility of electrolyte. Carbon blacks and activatedcarbons with surface areas between 200-2000 m²/g may be added inconjunction with graphite to improve surface area as well as electronicconductivity. Activated carbon is a form of carbon that has beenprocessed to greatly increase porosity, thus greatly increasing itssurface area (e.g., 1 gram of activated carbon may have surface area inexcess of 500 m²).

Numerous attempts have been made to overcome the above-mentionedproblems. For example, U.S. Pat. No. 6,548,211 to Kamada, et al.,discloses the addition of graphite powder having a mean particle sizesmaller than 30 μm added in the range of about 0.3% to 2% by weight.U.S. Patent Publication No. 2010/0015531 to Dickinson, et al., disclosesa paste for negative plate of lead acid battery having a activatedcarbon additive loadings of 1.0% to 2.0% by weight. The activated carbonadditive, taught by Dickinson, has a mesopore volume of greater thanabout 0.1 cm³/g and a mesopore size range of about 20-320 angstroms (Å)as determined by the DFT nitrogen adsorption method. U.S. PatentPublication No. 2010/0040950 to Buiel, et al. describes a negativeelectrode having a mixture of activated carbon (˜5-95% by weight), lead(5-95% by weight), and conductive carbon (5-20% by weight). U.S. Pat.No. 5,547,783 to Funato, et al., describes various additives, includingcarbon, acetylene black, polyaniline, tin powder, and tin compoundpowder having an average particle diameter of 100 μm or less. U.S. Pat.No. 5,156,935 to Hohjo, et al., describes electro-conductive whiskersmade of carbon, graphite or potassium titanate—useful as additives forthe negative plate of a lead-acid battery—having a diameter of 10 μm orless, aspect ratio of 50 or more, and a specific surface area of 2m²/g(21). Unfortunately, none of these previous attempts have been ableto achieve the benefit of both higher surface area and higher electronicconductivity in a single carbon material.

Carbon blacks and activated carbons have the ability to accept a highercharge because of their higher surface areas and enhanced electrolyteaccessibility. Unfortunately, because of their porous structures, carbonblacks and activated carbons have poor retention on particle size duringpaste mixing and cycling. As a result, carbon blacks and activatedcarbons often disintegrate, causing the carbon to bleed out of the plateover period of time, resulting in active material shedding from thegrids.

Graphites, by contrast, with ordered structures, are advantageousbecause they are both inert to electrochemical reactions duringcharge-discharge cycles and resist disintegration during cycle lifetests over an extended period. Unfortunately, graphites have lowersurface areas, thus restricting electrolyte access and resulting in anactive material with lower charge acceptance.

Despite the numerous existing battery additives, there is a need for animproved battery additive that (i) is inert to electrochemical reactionsduring charge-discharge cycles; (ii) resists disintegration during cyclelife tests over an extended period; and (iii) yields an increased chargeacceptance.

SUMMARY OF THE INVENTION

A graphitic carbon with a greater degree of defective sites in regulargraphene layers is disclosed herein. Lower regularity of graphiticlayers results in graphite with an advantageous surface area of, e.g.,about 300 m²/g, as compared to typical graphite surface areas, which arebetween 10 and 30 m²/g.

According to a first aspect of the present invention, an energy storagedevice comprises: an electrode comprising lead; an electrode comprisinglead dioxide; a separator between the electrode comprising lead and theelectrode comprising lead dioxide; an aqueous solution electrolytecontaining sulfuric acid; and a carbon-based additive having a specificsurface area of approximately 100 to 900 m²/g. Other exemplaryembodiments provide a carbon-based additive having a specific surfacearea of approximately 100 to 550 m²/g. Other exemplary embodimentsprovide a carbon-based additive having a specific surface area ofapproximately 100 to 350 m²/g. Other exemplary embodiments provide acarbon-based additive having a specific surface area of approximately200 to 550 m²/g. Other exemplary embodiments provide a carbon-basedadditive having a specific surface area of approximately 200 to 350m²/g.

According to a second aspect of the present invention, a paste suitablefor a negative plate of battery that includes a carbon-based additiveand has a surface area of at least 3 m²/g when an amount of the carbonadditive in the paste is approximately 0.3 to 6% by weight. Otherexemplary embodiments provide a paste suitable for a negative plate ofbattery that includes a carbon-based additive and has a surface area ofat least 3 m²/g when an amount of the carbon additive in the paste isapproximately 0.3 to 3% by weight. Other exemplary embodiments provide apaste suitable for a negative plate of battery that includes acarbon-based additive and has a surface area of at least 3 m²/g when anamount of the carbon additive in the paste is approximately 0.3 to 2% byweight. Other exemplary embodiments provide a paste suitable for anegative plate of battery that includes a carbon-based additive and hasa surface area of at least 3 m²/g when an amount of the carbon additivein the paste is approximately 0.3 to 1.5% by weight.

According to a third aspect of the present invention, a batteryincluding a negative plate comprises: a negative active material havinga surface area of at least 3 m²/g when an amount of the carbon-basedadditive in a paste is approximately 0.3 to 6% by weight. Otherexemplary embodiments provide a negative active material having asurface area of at least 3 m²/g when an amount of the carbon-basedadditive in a paste is approximately 0.3 to 3% by weight. Otherexemplary embodiments provide a negative active material having asurface area of at least 3 m²/g when an amount of the carbon-basedadditive in a paste is approximately 0.3 to 2% by weight. Otherexemplary embodiments provide a negative active material having asurface area of at least 3 m²/g when an amount of the carbon-basedadditive in a paste is approximately 0.3 to 1.5% by weight.

In certain embodiments, the carbon-based additive may be a graphitematerial having a specific surface area of approximately 100 to 900 m²/gand may be mixed with a negative, dry, unformed paste having a surfacearea greater than 3 m²/g. The concentration of the carbon-based additiverelative to the paste may be approximately 0.3 to 6% by weight.

In other exemplary embodiments, the carbon-based additive may be agraphite material having a specific surface area of approximately 100 to550 m²/g and may be mixed with a negative, dry, unformed paste having asurface area greater than 3 m²/g. The concentration of the carbon-basedadditive relative to the paste may be approximately 0.3 to 3% by weight.

In other exemplary embodiments, the carbon-based additive may be agraphite material having a specific surface area of approximately 250 to550 m²/g and may be mixed with a negative, dry, unformed paste having asurface area greater than 3 m²/g. The concentration of the carbon-basedadditive relative to the paste may be approximately 0.3 to 3% by weight.

In other exemplary embodiments, the carbon-based additive may be agraphite material having a specific surface area of approximately 100 to350 m²/g and may be mixed with a negative, dry, unformed paste having asurface area greater than 3 m²/g. The concentration of the carbon-basedadditive relative to the paste may be approximately 0.3 to 2% by weight.

In other exemplary embodiments, the carbon-based additive may be agraphite material having a specific surface area of approximately 250 to350 m²/g and may be mixed with a negative, dry, unformed paste having asurface area greater than 3 m²/g. The concentration of the carbon-basedadditive relative to the paste may be approximately 0.3 to 2% by weight.

In other exemplary embodiments, the carbon-based additive may be agraphite material having a specific surface area of approximately 100 to250 m²/g and may be mixed with a negative, dry, unformed paste having asurface area greater than 3 m²/g. The concentration of the carbon-basedadditive relative to the paste may be approximately 0.3 to 2% by weight.

In other exemplary embodiments, the carbon-based additive may be agraphite material having a specific surface area of approximately 100 to250 m²/g and may be mixed with a negative, dry, unformed paste having asurface area greater than 3 m²/g. The concentration of the carbon-basedadditive relative to the paste may be approximately 0.3 to 1.5% byweight.

In alternative embodiments, the carbon-based additive may be adisordered carbon additive (including, for example, Advanced Graphite)in negative active material with (i) crystallinity of 60% or lower, (ii)degradation onset temperature of 650° C. or lower; and (iii) degradationtemperature range of a minimum 170° C. or higher.

The carbon-based additive of the forgoing may also be used in a pastefor a negative plate of battery and further may have: (A) a total porevolume of greater than about 0.2 cm³/g with a predominant pore size ofless than 20 Å; (B) a total pore volume of greater than about 0.2 cm³/gwith a predominant pore size of 20 Å-500 Å; and/or (C) a total porevolume comprising (i) between about 20 and 40 percent microporous carbonparticles of the total amount of carbon-based additive by weight; (ii)between about 60 and 70 percent mesoporous carbon particles of the totalamount of carbon-based additive by weight; and (iii) between about 0 and10 percent macroporous carbon particles of the total amount ofcarbon-based additive by weight.

According to a fourth aspect of the present invention, a methodcomprises the steps of introducing carbon-based particles into a pastemix to form a carbon paste material, the carbon-based particles having aspecific surface area of approximately 100 to 900 m²/g; providing thecarbon paste material on a battery grid; and curing the paste material.In other exemplary embodiments, the carbon-based particles have aspecific surface area of approximately 100 to 550 m²/g. In otherexemplary embodiments, the carbon-based particles have a specificsurface area of approximately 100 to 350 m²/g. In other exemplaryembodiments, the carbon-based particles have a specific surface area ofapproximately 100 to 250 m²/g.

As a result of the forgoing, in exemplary embodiments, the chargeacceptance power of a battery or energy storage device improves by 50%or greater at all states-of-charge, and discharge power improves up to35% with greater improvements at lower states-of-charge compared tostandard, no-carbon batteries. Exemplary Advanced Graphite containinggroups have 50% or higher charging current under micro-hybrid dynamiccharge acceptance test (mDCAT) test and last at least twice as manycycles as compared to standard, no-carbon batteries.

DESCRIPTION OF THE DRAWINGS

The patent application file contains at least one drawing executed incolor. Copies of this patent application publication with colordrawing(s) will be provided by the U.S. Patent and Trademark Office uponrequest and payment of the necessary fees.

These and other advantages of the present invention will be readilyunderstood with reference to the following specifications and attacheddrawings wherein:

FIG. 1 a is a graph representing the extent of periodic graphene layerscompared by two-dimensional, wide-angle X-ray diffraction;

FIG. 1 b is a graph representing the extent of periodic graphene layerscompared by thermogravimetric analysis for the standard, battery-gradegraphite and Advanced Graphite used in this work;

FIG. 1 c is a chart depicting wide-angle X-ray diffraction andthermogravimetric analysis results of standard, battery-grade graphiteand Advanced Graphite;

FIG. 1 d is a chart depicting initial characterization of spiral 6V/25Ah modules;

FIG. 2 a is a graph representing pore-volume distribution calculated bydensity functional theory (DFT) method for standard, battery-gradegraphite;

FIG. 2 b is a graph representing pore-volume distribution calculated bydensity-functional theory (DFT) method for Advanced Graphite;

FIG. 3 a is a bar graph representing regenerative-charge acceptance;

FIG. 3 b is a bar graph representing peak power for 6V/24 Ah modulescontaining (i) no-carbon, standard, negative mix; (ii) negative mix with1% by weight standard graphite and 1 wt % standard carbon black; and(iii) negative mix with 2% by weight-advanced carbon at differentstate-of-charges (SoC) at 25° C.;

FIG. 4 is a graph representing charge current at 500th microcycle(end-of-test unit) in micro-hybrid dynamic charge acceptance test(mDCAT) for (i) no-carbon, standard, negative mix; (ii) negative mixwith 1% by weight standard graphite and 1% by weight standard carbonblack; and (iii) negative mix with 2% by weight advanced carbon withbatteries at 80% SoC;

FIG. 5 is a graph representing end of discharge voltage for (i) negativemix with 1% by weight standard graphite and 1 wt % standard carbonblack; and (ii) negative mix with 2% by weight-advanced carbon at 60%state-of-charges (SoC) and 2.5% depth-of-discharge (DoD) at 25° C. onnon-stop, power assist cycle life;

FIG. 6 is a diagram of an example prismatic lead-acid battery capable ofcarrying out the present invention;

FIG. 7 is a diagram of an example spiral-wound lead-acid battery capableof carrying out the present invention;

FIG. 8 is a diagram demonstrating a method of preparing an AdvanceGraphite paste and battery electrode;

FIG. 9 a shows a graph of discharge capacity for batteries with standardnegative mix with no carbon and batteries with advanced graphitecontaining negative mix;

FIG. 9 b shows a graph of EN Cold cranking test results for batterieswith standard negative mix with no carbon and batteries with advancedgraphite containing negative mix;

FIG. 10 a shows a graph of dynamic charge acceptance testing performedat 70% state of charges (SoC) with charge voltage of 13.5, 14.0 or 14.4V for batteries with standard negative mix with no carbon and forbatteries with advanced graphite containing negative mix;

FIG. 10 b shows a graph of dynamic charge acceptance testing performedat 80% state of charges (SoC) with charge voltage of 13.5, 14.0 or 14.4V for batteries with standard negative mix with no carbon and forbatteries with advanced graphite containing negative mix;

FIG. 10 c shows a graph of dynamic charge acceptance testing performedat 90% state of charges (SoC) with charge voltage of 13.5, 14.0 or 14.4V for batteries with standard negative mix with no carbon and forbatteries with advanced graphite containing negative mix;

FIG. 11 shows a graph of end of discharge voltages and dischargecapacities in VDA 17.5% DoD test for batteries with standard negativemix with no carbon and for batteries with advanced graphite containingnegative mix;

FIG. 12 a shows a graph of discharge capacity (C20 rate) test resultsfor batteries with standard negative mix with no carbon and forbatteries with advanced graphite containing negative mix;

FIG. 12 b shows a graph of reserve capacity test results for batterieswith standard negative mix with no carbon and for batteries withadvanced graphite containing negative mix;

FIG. 12 c shows a graph of EN Cold cranking test results for batterieswith standard negative mix with no carbon and for batteries withadvanced graphite containing negative mix; and

FIG. 13 shows a graph of discharge capacities as % of rated capacityover 50 cycles of Repeated reserve capacity test for batteries withstandard negative mix with no carbon and for batteries with advancedgraphite containing negative mix.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail because they would obscure the invention inunnecessary detail.

A graphitic carbon with a greater degree of defective sites in regulargraphene layers is disclosed herein. Lower regularity of graphiticlayers results in an Advanced Graphite with a highly advantageoussurface area, e.g., about 100-900 m²/g, as compared to typical numbersof between 10-30 m²/g. A carbon based additive (e.g., Advance Graphite)would preferably have a surface area between 20 and 750 m²/g with a morepreferred range of about 20-450 m2/g or 20-550 m²/g. However, a mostpreferred range would be about 100-900 m²/g, 100-550 m²/g, 100-350 m²/gor 100-250 m²/g. A suitable off-the-shelf Advanced Graphite substitutemay include, for example, CyPbrid I™ and CyPbrid II™. CyPbrid I™,available from Imerys Graphite and Carbon™ (www.timcal.com), is a highpurity graphite (<0.22% ash) with a specific surface area of 280-300m²g. Alternatively, carbon nanotubes may be used as a carbon-based pasteadditive. Carbon nanotubes are hexagonally shaped arrangements of carbonatoms that have been rolled into molecular-scale tubes of graphiticcarbon. Carbon nanotubes have been constructed with length-to-diameterratio of up to 132,000,000:1, therefore yielding a very high surfacearea to volume ratio. In other alternate exemplary embodiments, one ofthe following can be used in negative active paste: an admixture ofcrystalline carbon, like graphite, carbon nanotube or graphene andamorphous carbon, like carbon black or activated carbon; or heat and/ormechanically treated crystalline carbon, like graphite, carbon nanotubeor grapheme, among others.

During research and development of the Advanced Graphite and AdvancedGraphite paste, a number of experimental methods and devices wereemployed: (i) the structures of graphite powder samples were analyzedusing X-ray diffraction; (ii) degradation behavior was examined using athermogravimetric analyzer; and (iii) surface area and pore-sizedistribution were probed using a surface area analyzer. Powder X-raydiffraction was performed using a Siemens D5000 X-Ray Diffractometeroperated at 20 kV, 5 A. Thermogravimetric analysis (TGA) was performedusing a TA instruments TGA Q500 by heating the graphite powder sample upto 1,000° C. at the rate of 20° C./min. Surface area and pore-sizedistribution were measured using nitrogen gas adsorption on aMicromeritics Tristar 3020. Data were analyzed using Brunauer, Emmett,and Teller (BET) and density functional theory (DFT) methods.

Referring first to FIG. 2 a, a graph representing pore-volumedistribution calculated by the DFT method for a standard, battery-gradegraphite is shown, while FIG. 2 b represents the pore-volumedistribution for Advanced Graphite.

FIG. 2 a shows that the pore volume for standard graphite is relativelylow (less than 4.5×10⁻³ cm³/g) for the entire range of pores measuredfor nitrogen gas adsorption with a wide pore range distribution. As aresult, the surface area of standard graphite is relatively low, thusrestricting electrolyte access, resulting in an active material withlower charge acceptance.

FIG. 2 b, by contrast, shows that Advanced Graphite has a much higherpore volume for pore widths (0-800 Å) with a peak of 0.05 cm³/g withpredominantly micro (less than 20 Å) and meso (20-500 Å) porosity.Depending on the batch, Advanced Graphite may further contain a trivialamount of macro (greater than 500 Å) pore widths, typically between 0and 10%. Advanced Graphite with predominantly micro and meso porosityhas a total pore volume approximately 3 times greater than standardgraphite (0.2 cm³/g for advanced graphite vs. 0.065 cm³/g for standardgraphite). As a result, the surface area of standard graphite is muchgreater, thus allowing electrolyte access, resulting in an activematerial with higher charge acceptance. To test and compare the AdvancedGraphite against various negative pastes, spiral wound 6V/25 Ah modulesand prismatic 14.4V/78 Ah valve-regulated lead-acid (VRLA) type absorbedglass mat (AGM) batteries were assembled with three differentcompositions of negative paste, including (i) a control negative mixhaving no additional carbon; (ii) a negative mix with 1%-by-weightstandard graphite and 1%-by-weight, standard carbon black; and (iii) anegative mix with 2% by weight Advanced Graphite. AGM batteries, insteadof using a gel or liquid electrolyte, use a fiberglass like separator tohold the electrolyte in place. The physical bond between the separatorfibers, the lead plates, and the container make AGMs spill-proof and themost vibration and impact resistant lead-acid batteries available today.Even better, AGM batteries use almost the same voltage set-points asflooded cells and thus can be used as drop-in replacements for floodedcells.

Initial characterization of the modules included 20-hour capacity(discharge at 1.2 A to 5.25V at 25° C.), reserve capacity (discharge at25 A to 5.25V at 25° C.) and cold cranking (discharge at 400 A to 3.6Vat −18° C.). After each test, the modules were recharged at 6 A/7.2V/20h+4 h/0.6 A. For the sake of accuracy during the testing, batteryweights, internal resistance, and low-rate and high-rate discharges foreach group were equivalent at onset. The average results for the initialcharacterizations of the modules of the three groups of modules aresummarized in FIG. 1 d. FIG. 1 d clearly show that all batteries hadcomparable initial performance parameters, thus suggesting that anychange in performance during the testing would be due to the variouspaste additives, and not variations in the battery construction.

In hybrid electric vehicle applications, the power on discharge for abattery and the charge acceptance power are of great importance.Discharge power determines the degree of achievable electrical boostingduring the acceleration period, while the charge acceptance affects thedegree of utilization of the regenerative braking energy during thedeceleration step. To simulate the different conditions in which thebattery can work in the vehicle, the tests were conducted at differentState-of-Charge's (SoC) ranging from 20% to 100%. A constant voltage of16V was used for 5 seconds at 25° C. for charge acceptance power while avoltage of 10V was used for 10 seconds at 25° C. for discharge powermeasurement.

A Micro-hybrid dynamic charge acceptance test (mDCAT) was performed onprismatic batteries at 80% SoC. The test cycle included multiplemicro-cycles with different discharge currents (i.e., discharge at 48 Afor 60 s, discharge at 300 A for 1 s, rest for 10 s, charge at 100 A to100% SoC, discharge at 7 A for 60 s and rest for 10 s) including a highcurrent pulse. The test cycle included a total of 500 microcycles with 6hour rest time.

Power-assist, cycle life tests were also performed to determine theinfluence of the three different negative plate formulations in theevolution of capacity, voltage, and internal resistance under partialstate-of-charge cycling. The profile used for testing was based on theEuropean Council for Automotive R&D (EUCAR) procedure for HybridElectric Vehicles (HEV) and had to be repeated 10,000 times (on oneunit) with the battery at 60% SoC and 2.5% depth-of-discharge.

The evolution of end voltage, capacity, weight loss, and internalresistance is recorded every 10,000 cycles. The battery was rested for 6hours after every 10,000 cycles to allow the electrolyte to stabilize.At end of discharge, a voltage of 5V (per 6V module) reached along thecycling, or a battery capacity under 50% of initial value, wasconsidered battery failure criteria. From previous Advanced Lead-AcidBattery Consortium (ALABC) reports, power-assist cycle life in the range200,000-220,000 cycles has been obtained for different NAM formulationsthat included additions of different types of graphites and combinationcarbon black and graphite in the range 1%-1.5%. A non-stop,power-assist, cycle-life test, in which the battery is cycledcontinuously without rest step at 10,000 cycle intervals, has beendevised to simulate real life test conditions. This test helps indifferentiating the various grades of carbons that produced similar testin a standard, EUCAR, power-assist cycle-life test.

The results show the negative mix with 2% by weight Advanced Graphitegreatly outperformed both the standard negative mix and the negative mixwith 1% by weight Standard Graphite and 1% by weight Standard CarbonBlack. In reviewing the results, a wide-angle X-ray diffraction (WAXD)was used to determine the regularity of carbon structures. Diffractionpeaks at a specific angle appeared due to constructive interferencesfrom X-rays diffracted from periodic crystal structures. For graphite,the only periodic structure is the arrangement of graphene sheets in thez-direction. The distance between these carbon layers is a constant˜3.35 Å. Diffraction from these sheets (002 plane) of graphite resultsin a diffraction peak at 2θ˜26°.

A crystalline solid consists of regularly spaced atoms (electrons) thatmay be described using imaginary planes. The distance between theseplanes is called the d-spacing, where the intensity of the d-spacepattern is typically directly proportional to the number of electrons(atoms) that are found in the imaginary planes. Every crystalline solidwill have a unique pattern of d-spacing (also known as the powderpattern), which may be analogous to a “fingerprint” for a solid. Thepeak position and d-spacing remains constant for all grades of graphite,while intensity of the peak varies based on the amount of defectspresent in the sample, quantified by crystallinity percentage of thesample. Carbon black (and activated carbon) has no peak due to theabsence of periodic structure. Full width at half maximum (FWHM) of apeak is a measure of crystal size distribution, whereas a smaller FWHM(narrow peak) corresponds to smaller distribution of crystal sizes.Surface area is, in general, inversely related to crystallinitypercentages (lower defects in carbon, lower surface area).

WAXD and TGA results for standard battery grade graphite, as well as theAdvanced Graphite of the present application, are provided in FIGS. 1 athrough 1 d. Diffraction peak position (20˜26°), as well as d-spacing(3.4 Å), for two grades were consistent with diffraction patterns fromgraphene layers. The peak intensity for the disclosed Advanced Graphitewas about ˜70% of standard battery grade graphite, indicating greaterdefects on graphite structures. The chart in FIG. 1 c represents acomparison of the wide-angle x-ray diffraction and thermogravimetricanalysis results of standard battery grade graphite and AdvancedGraphite.

As indicated in FIG. 1 c, Advanced Graphite also has a lowercrystallinity percentage (60%) and a wider full width at half maximum(FWHM) value (0.79) (i.e., larger size distribution) compared tostandard graphite, yielding higher defective carbon sites. The lowercrystallinity percentage indicates higher defects in the AdvanceGraphite structure, providing a significantly greater surface area.Advanced Graphite's surface area was found to be over ten times greaterthan the surface area of standard graphite (330 m²/g versus 21 m²/g).Despite the higher surface area, the positive attributes of advancedgraphite remained virtually unchanged. For example, according to thethermogravimetry tests, both standard graphite and Advanced Graphite hadcomparable degradation values, indicating that, unlike high surface areacarbon black and activated carbon, the graphite will not degrade as muchover time. Essentially, Advanced Graphite combines the stability ofstandard graphite with the high surface area of carbon blacks andactivated carbons in a single carbon-based additive.

Advanced Graphite also onsets degradation at a lower temperature ascompared to standard graphite, resulting from the presence of higheramorphous carbons and/or defective carbon sites (as seen in FIG. 1 b).FIG. 1 a is a graph representing the extent of periodic graphene layerscompared by two-dimensional, wide-angle x-ray diffraction, while FIG. 1b represents the extent of periodic graphene layers compared bythermogravimetric analysis for the standard battery grade graphite andAdvanced Graphite of the present invention. Wider degradation window forAdvanced Graphite is consistent with wider FWHM result obtained fromWAXD, indicating large crystal size distribution.

The charge acceptance power and power discharge at different SoC (at aconstant 25° C.) are presented in FIGS. 3 a and 3 b for modulescontaining: (i) no-carbon, standard-negative mix; (ii) negative mix with1% by weight standard graphite and 1 wt % standard carbon black; and(iii) negative mix with 2% by weight advanced carbon. FIG. 3 a is a bargraph representing regenerative charge acceptance (watts), while FIG. 3b is a bar graph representing peak power (watts) for 6V/24 Ah. The datawas collected at different state-of-charge (SoC) values, ranging from20% to 100% with 20% intervals. For reference, FIG. 1 d is a chartdepicting the comparable initial characterization of three spiral 6V/25Ah modules used in the test.

Referring first to FIG. 3 a, the graph indicates that a standard,graphite-carbon mix generally shows a higher charge acceptance ascompared to both the no-carbon control mix and Advanced Graphite mix.The performance of the standard, graphite-carbon mix may be attributedto the presence of smaller-particulate, high surface area, carbon black.

In FIG. 3 b, by contrast, the graph clearly indicates that the AdvancedGraphite mix consistently yields the highest discharge power at allstate-of-charge levels. The graph also shows the drastic drop indischarge power for the no-carbon, control mix and standard,graphite-carbon mix as the SOC decreases from 100% to 20%. The AdvancedGraphite mix's outstanding performance may be attributed to the higherelectrical conductivity of Advanced Graphite as compared to the standardgraphite/carbon black mix. Remarkably, maximum improvement was observedat 20% SoC, where the Advanced Graphite mix showed more than 35% and 25%improvement over the control battery (no-carbon mix) and standard,graphite-carbon mix, respectively.

A micro-hybrid dynamic charge acceptance test (mDCAT) was performed onprismatic batteries (e.g., a battery that is prismatic, or rectangular,in shape rather than cylindrical) at 80% SoC to determine chargeacceptance capability of batteries in hybrid electric vehicle (HEV)application at high rate partial state-of-charge (SoC) conditions.Charge current at 500th micro-cycle or end of test unit for differentbatteries at 25° C. is presented in FIG. 4. The results show highercharging current representing higher charge acceptance for bothcarbon-containing groups compared to standard, no-carbon batteries. Thecontrol batteries reached end-of-test condition after 13 units ofcycling (6,500 cycles), while carbon-containing batteries continued tocycle beyond 10,000 cycles, representing longer cycle life.

The EUCAR, power-assist, cycle-life test is an important test for hybridelectric vehicle (HEV) applications carried out to simulate the powerperformance of batteries under partial state-of-charge cycling. Theprofile used for testing contains a test unit that repeats 10,000 timeswith the battery at 60% SoC and 2.5% depth-of-discharge. The batteryrests for a few hours after 10,000 cycles for the electrolyte tostabilize in the battery before further testing. This rest step inpower-assist cycle-life tests does not typically represent actual useconditions. Therefore, a non-stop, power-assist, cycle-life test wasdevised, whereby the battery was cycled without rest until it reachedfailure condition. The non-stop, power-assist test also helps todifferentiate various carbon groups that perform alike when rested afterevery 10,000 cycles.

Results of the non-stop, power-assist test is presented in FIG. 5, whichshows the standard, graphite-carbon mix (1% by weight standard graphiteand 1% by weight standard carbon black and a negative mix with 2% byweight advanced carbon)—the best performing group from previousresults—reaching failure condition below 20,000 cycles. A significantand unexpected cycle life was achieved for the Advanced Graphite mix (2%by weight Advanced Graphite), where the battery was able to cycle beyond145,000 cycles above the failure voltage of 9V. This importantadvancement in cycle life is the result of combining two importantattributes of additives—higher surface area and higher electricalconductivity in a single graphite (i.e., Advanced Graphite).

Elimination of carbon black, with its inferior mechanical stability,from the negative paste mix, a typical additive to improve surface areaand enhance charge acceptance, results in a robust battery that may becycled efficiently over an extended period of time.

Advanced Graphite, with ordered structures that are inert toelectrochemical reactions during charge-discharge cycles and withsurface area of at least ten times greater than typical battery-gradenatural or synthetic graphites, is an ideal candidate for lead-acidbattery application. The use of this Advanced Graphite will advance thecapabilities of valve-regulated, lead-acid battery to compete with otherchemistries for HEV application.

FIG. 6 illustrates a prismatic lead-acid battery 600 configured toaccept an Advanced Carbon paste. As seen in the diagram, the lead-acidbattery comprises a lower housing 610 and a lid 616. The cavity formedby the lower housing 610 and a lid 616 houses a series of plates thatcollectively form a positive plate pack 612 (i.e., positive electrode)and a negative plate pack 614 (i.e., negative electrode). The positiveand negative electrodes are submerged in an electrolyte bath within thehousing. Electrode plates are isolated from one another by a porousseparator 606 whose primary role is to eliminate all contact between thepositive plates 604 and negative plates 608, while keeping them within aminimal distance (e.g., a few millimeters) of each other. The positiveplate pack 612 and negative plate pack 614 each have an electricallyconnective bar travelling perpendicular to the plate direction thatcauses all positive plates to be electrically coupled and negativeplates to be electrically coupled, typically by a tab on each plate.Electrically coupled to each connective bar is a connection post orterminal (i.e., positive 620 and negative post 618). The Advanced Carbonpaste of the present application may be pressed in to the openings ofgrid plates 602, which, in certain exemplary embodiments, may beslightly tapered on each side to better retain the paste. Although aprismatic AGM lead-acid battery is depicted, the Advance Carbon additivemay be used with any lead-acid battery, including, for example,flooded/wet cells and/or gel cells. As seen in FIG. 7, the battery shapeneed not be prismatic, it may be cylindrical, or a series of cylindricalcells arranged in various configurations (e.g., a six-pack or an off-setsix-pack).

A carbon containing paste may be prepared having an optimum viscosity(260-310 grams/cubic inch) and penetration (38-50). The carbon paste maythen be applied to a lead alloy grid that may be cured at a hightemperature and humidity. In cylindrical cells, positive and negativeplates are rolled with a seperator and/or pasting papers into spiralcells prior to curing. Once cured, the plates are further dried at ahigher temperature and assembled in the battery casing. Respectivegravity acid may be used to fill the battery casing. Batteries are thenformed using an optimized carbon batteries formation process (i.e.,profile). The formation process may include, for example, a series ofconstant current or constant voltage charging steps performed on abattery after acid filling to convert lead oxide to lead dioxide inpositive plate and lead oxide to metallic lead in negative plate. Ingeneral, carbon-containing negative plates have lower active material(lead oxide) compared to control plates. Thus, the formation process(i.e., profile) for carbon containing plates is typically shorter.

FIG. 7 illustrates a spiral-wound lead-acid battery 700 configured toaccept an Advanced Graphite paste. As in the prismatic lead-acid battery600, a spiral-wound lead-acid battery 700 comprises a lower housing 710and a lid 716. The cavity formed by the lower housing 710 and a lid 716houses one or more tightly compressed cells 702. Each tightly compressedcell 702 has a positive electrode sheet 704, a negative electrode sheet708 and a separator 706 (e.g., an absorbent glass mat separator). AGMbatteries use thin, sponge—like, absorbent glass mat separators 706 thatabsorb all liquid electrolytes while isolating the electrode sheets. Acarbon containing paste may be prepared having an optimum viscosity(260-310 grams/cubic inch) and penetration (38-50). The carbon paste maythen be applied to a lead alloy grid that may be cured at a hightemperature and humidity. In cylindrical cells, positive and negativeplates are rolled with a seperator and/or pasting papers into spiralcells prior to curing. Once cured, the plates are further dried at ahigher temperature and assembled in the battery casing. Respectivegravity acid may be used to fill the battery casing. Batteries are thenformed using an optimized carbon batteries formation process.

The Advanced Graphite paste may be prepared using one of many knownprocesses. For example, U.S. Pat. No. 6,531,248 to Zguris et al.discusses a number of known procedures for preparing paste and applyingpaste to an electrode. For example, a paste may be prepared by mixingsulfuric acid, water, and various additives (e.g., Advance Graphiteand/or other expanders), where paste mixing is controlled by adding orreducing fluids (e.g., H₂O, H₂SO₄, tetrabasic lead sulfate, etc.) toachieve a desired paste density. The paste density may be measured usinga cup with a hemispherical cavity, penetrometer (a device often used totest the strength of soil) and/or other density measurement device. Anumber of factors can affect paste density, including for example, thetotal amount of water and acid used in the paste, the specific identityof the oxide or oxides used, and the type of mixer used. Zguris alsodiscusses a number of methods for applying a paste to a batteryelectrode. For example, a “hydroset” cure involves subjecting pastedplates to a temperature (e.g., between 25 and 40° C.) for 1 to 3 days.During the curing step, the lead content of the active material isreduced by gradual oxidation from about 10 to less than 3 weightpercent. Furthermore, the water (i.e., about 50 volume percentage) isevaporated.

FIG. 8 is a flow chart demonstrating a method of preparing an AdvancedGraphite paste and applying it to a battery electrode. To form thepaste, paste ingredients (e.g., Advanced Graphite, graphite, carbonblack, lignin derivatives, BaSO₄, H₂SO₄, H₂O, etc.) are mixed 800 untila desired density (e.g., 4.0 to 4.3 g/cc) is determined. The carboncontaining paste may be prepared by adding lead oxide, one or morecarbon expanders and polymeric fibers to a mixing vessel, with mixing ofthe materials for 5-10 minutes using a paddle type mixer (800). Watermay be added (x % more water than regular negative paste mix for every1% additional carbon) with continued mixing. A carbon paste (e.g., apaste containing Advance Graphite) would preferably contain 0.3-6%carbon-based additive by weight with exemplary ranges of about 1-4% or1-3%. Other exemplary embodiments describe a carbon paste would containabout 0.3-6%, 0.3-3%, 0.3-2% or 0.3-1.5% carbon-based additive byweight.

Once the carbon containing paste has been prepared, sulfuric acid may besprinkled into the mixing vessel with constant stirring; and mixing maybe continued for additional 5-10 minutes (802). Viscosity andpenetration of the resulting carbon paste may be measured and water maybe added to the paste to attain necessary visosity (804). This carboncontaining paste may then be applied to lead alloy grid (806) followedby curing at high temperature and humidity (808). In cylindrical cells,the positive and negative plates are rolled with a seperator and/orpasting papers into spiral cells before curing. Cured plates are furtherdried at higher temperature. Dried plates are assembled in the batterycasing; and respective gravity acid is filled into the battery casing(810). Batteries are then formed using an optimized carbon batteriesformation profile (812).

Additional Examples follow:

EXAMPLE 1

Group L3 70 Ah Micro-hybrid flooded (MHF) prismatic type batteries wereassembled with two different compositions of negative paste: standardnegative mix with no additional carbon; and negative mix with 1.3 wt %Advanced Graphite

A standard paste-mixing recipe was used for standard positive andstandard negative control pastes. Additional graphite containing carbonadditive was added to the negative paste mix for advanced graphitecontaining plates. Advanced graphite containing paste was prepared byadding lead oxide, one or more carbon expanders and polymeric fibers toa mixing vessel, followed by mixing of the materials for several minutesusing a standard batch paste mixer. Additional water was used foradvanced graphite containing paste. Sulfuric acid was sprinkled into themixing vessel with constant stirring and the mixing was continued for anadditional time.

Viscosity and penetration of the resulting carbon paste was measured,and optionally, water was added to the paste to attain the desiredviscosity. This carbon-containing paste was then applied onto a leadalloy grid, followed by curing at high temperature and humidity. Similarprocedures were followed for standard positive and standard negativeplates using standard paste recipe, paste mixing, pasting and curingprocess. The dried plates were assembled in the battery casing withstandard seperators; and standard specific gravity acid was filled intothe battery casing specific to MHF batteries. Batteries were then formedusing an optimized carbon battery formation profile. Formed batterieswere subjected to various electrochemical tests below.

Initial characterization of group L3 batteries included a 20-hourdischarge capacity test and a EN cold cranking test. After each test,the modules were recharged at conditions recommended for the batterytype. These tests were performed to determine the responses of batteryto slow as well as to fast discharge conditions.

FIG. 9 a shows a graph of discharge capacity for batteries with standardnegative mix with no carbon and batteries with advanced graphitecontaining negative mix. FIG. 9 b shows a graph of EN Cold cranking testresults for batteries with standard negative mix with no carbon andbatteries with advanced graphite containing negative mix FIGS. 9 a and 9b show that both standard batteries with no additional carbon as well asbatteries with 1.3% advanced graphite additive meet or exceed the L3group battery specification for discharge capacity (70 Ah) and EN CCAtest specification of 7.5V at 10 seconds and 9.0V at 40 seconds.

Charge acceptance test was performed to determine the ability of batteryto accept charge at a partial state of charge (PSoC) conditions. Thebattery was initially discharged at C/20 rate to get the battery to 70,80 or 90% state of charge (SoC). After the battery voltage stabilized atthat PSoC, battery was charged with a constant voltage. Current drawn bybatteries during this charge step was monitored and recorded. The chargecurrent that a battery accepted during this test depended on surfacearea of the negative active material and electrical conductivity of theelectrodes. Charge acceptance varied with charge voltage, as well asSoC, of the battery. Charge voltages of 13.5, 14.0 and 14.4 V were usedto determine the charge acceptance of batteries at 70, 80 or 90% SoC(FIGS. 10 a, 10 b and 10 c),

Advanced graphite-containing batteries showed higher charge acceptance,compared to standard batteries with no carbon, at all charge voltage andat all SoC. Differences in charge acceptance for standard and advancedgraphite containing batteries appear to be higher at higher testvoltages. Similar differences in charge acceptance were observed at allstate-of-charges. Charge acceptance decreased for both groups at lowertest voltages.

Standard batteries with no carbon, and batteries with advanced graphiteadditives, were then subjected to 17.5% depth of discharge (DoD) testaccording to the Verband der Automobilindustrie (VDA) performancespecification for enhanced flooded batteries. One unit (approximately 1week) of 17.5% DoD testing consists of a discharge capacity test doneafter 85 charge—discharge micro-cycles, with 17.5% depth of dischargeswing performed on a battery at 50% state of charge. FIG. 11 shows thata significant and unexpected cycle life was achieved for the advancedgraphite mix where the battery was able to cycle more than 1000 cycles(13 to 14 weeks), while the standard batteries failed around 750 cycles(less than 9 weeks). This important advancement in cycle life is theresult of combining two important attributes of additives—higher surfacearea and higher electrical conductivity in single graphite. Addition ofthis advanced graphite results in a robust battery that could be cycledefficiently over an extended period of time.

Discovery of this advanced graphite, with ordered structures that areinert to electrochemical reactions during charge-discharge cycles andwith surface area of at least 10 times greater than typical batterygrade natural or synthetic graphites, is a vital step for lead acidbattery application. Use of this Advanced Graphite represents asignificant advance for the capabilities of valve-regulated lead acidbattery as compared with other chemistries for HEV application.

EXAMPLE 2

Group LN5 92 Ah Advanced glass mat (AGM) type prismatic batteries wereassembled with two different compositions of negative paste. Tests wereconducted with regard to batteries having no additional carbon standardnegative mix for reference, as well as negative mix with 0.3 wt %Advanced Graphite. A standard paste-mixing recipe was used for standardpositive and standard negative control pastes. Additionalgraphite-containing carbon additive was added to the negative paste mixfor advanced graphite-containing plates. The dried plates were assembledin the battery casing with standard AGM seperators; and standardspecific gravity acid was filled into the battery casing specific to AGMbatteries. Formed batteries were subjected to various electrochemicaltests, as is described below.

Initial characterization of group LN5 batteries included a 20-hourdischarge capacity test (FIG. 12 a), a Reserve capacity test (FIG. 12 b)and a EN cold cranking test (FIG. 12 c). After each test, the moduleswere recharged at conditions recommended for the battery type. Thesetests were performed to determine the responses of battery to slow,medium and fast discharge conditions. FIGS. 12 a, 12 b and 12 c showthat both standard batteries with no additional carbon, as well asbatteries with 0.3% advanced graphite additive, meet or exceed the LN5group battery specification for discharge capacity (92 Ah), reservecapacity (160 minutes) and EN CCA test specification of 7.5V at 10seconds and 9.0V at 40 seconds.

Repeated reserve capacity test is a cycle life test performed to predictthe durability of lead acid batteries. The batteries are cycled atreserve capacity rate (25 A discharge) 50 times. Discharge capacitiesare monitored and recorded over 50 cycles for both standard and advancedgraphite batteries. FIG. 13 shows a graph of discharge capacities as %of rated capacity over 50 cycles of Repeated reserve capacity test forbatteries with standard negative mix with no carbon and for batterieswith advanced graphite containing negative mix. FIG. 13 show thatAdvanced Graphite containing battery increases cumulative energycapacity over 50 cycles of repeated reserve capacity test by about 10%,when compared to standard battery. This increase is observed for anaverage of 3 batteries from each group. This advancement in cycle lifeis the result of combining two important attributes of advanced graphiteadditive-higher surface area and higher electrical conductivity insingle graphite.

The individual components shown in outline or designated by blocks inthe attached Drawings are all well-known in the battery arts, and theirspecific construction and operation are not critical to the operation orbest mode for carrying out the invention.

While the present invention has been described with respect to exemplaryembodiments, it is to be understood that the invention is not limited tothe disclosed embodiments. To the contrary, the invention is intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims. The scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structures and functions.

All U.S. and foreign patent documents, all articles, brochures, and allother published documents discussed above are hereby incorporated byreference into the Detailed Description of the Preferred Embodiment.

What is claimed is:
 1. An energy storage device, comprising: anelectrode comprising lead; an electrode comprising lead dioxide; aseparator between the electrode comprising lead and the electrodecomprising lead dioxide; an aqueous solution electrolyte containingsulfuric acid; and a carbon-based additive comprising graphite having aspecific surface area of approximately 100 to 900 m²/g, wherein thecarbon-based additive is a disordered carbon additive in negative activematerial with (i) crystallinity of 60% or lower, (ii) degradation onsettemperature of 650° C. or lower; and (iii) degradation temperature rangeof a minimum 170° C. or higher.
 2. The energy storage device of claim 1,wherein the carbon-based additive has a specific surface area ofsubstantially 100 to 550 m²/g.
 3. The energy storage device of claim 1,wherein the carbon-based additive has a specific surface area ofsubstantially 100 to 350 m²/g.
 4. The energy storage device of claim 1,wherein the carbon-based additive has a specific surface area ofsubstantially 100 to 250 m²/g.
 5. The energy storage device of claim 1,wherein the carbon-based additive is mixed with a negative, dry,unformed paste having a surface area greater than 3 m²/g.
 6. The energystorage device of claim 4, wherein the concentration of the carbon-basedadditive relative to the paste is approximately 0.3 to 6% by weight. 7.The energy storage device of claim 4, wherein the concentration of thecarbon-based additive relative to the paste is approximately 0.3 to 3%by weight.
 8. The energy storage device of claim 4, wherein theconcentration of the carbon-based additive relative to the paste isapproximately 0.3 to 2% by weight.
 9. The energy storage device of claim1, wherein the carbon-based additive is used in a paste for a negativeplate of battery and has a total pore volume of greater than about 0.2cm³/g with a predominant pore size of less than 20 Å.
 10. The energystorage device of claim 1 wherein the carbon-based additive is used in apaste for a negative plate of battery and has a total pore volume ofgreater than about 0.2 cm³/g with a predominant pore size of 20 Å-500 Å.11. An energy storage device, comprising: an electrode comprising lead;an electrode comprising lead dioxide; a separator between the electrodecomprising lead and the electrode comprising lead dioxide; an aqueoussolution electrolyte containing sulfuric acid; and a carbon-basedadditive comprising graphite having a specific surface area ofapproximately 100 to 900 m²/g, wherein the carbon-based additive has (i)between about 20 and 40 percent microporous carbon particles of thetotal amount of carbon-based additive by weight; (ii) between about 60and 70 percent mesoporous carbon particles of the total amount ofcarbon-based additive by weight; and (iii) between about 0 and 10percent macroporous carbon particles of the total amount of carbon-basedadditive by weight.
 12. The energy storage device of claim 11 whereinthe energy storage device is capable of at least 145,000 cycles in anon-stop, power-assist test.
 13. A battery, including a negative plate,comprising a carbon-based additive comprising graphite having a surfacearea of at least 3 m²/g when an amount of the carbon-based additive in apaste is approximately 0.3 to 6% by weight, wherein the carbon-basedadditive is a disordered carbon additive in negative active materialwith (i) crystallinity of 60% or lower, (ii) degradation onsettemperature of 650° C. or lower; and (iii) degradation temperature rangeof a minimum 170° C. or higher.
 14. The battery of claim 13, wherein thecarbon-based additive is a graphite additive having a specific surfacearea of approximately 100 to 550 m²/g.
 15. The battery of claim 13wherein the carbon-based additive is a graphite additive having aspecific surface area of approximately 100 to 350 m²/g.
 16. The batteryof claim 13 wherein the carbon-based additive is a graphite additivehaving a specific surface area of approximately 100 to 250 m²/g.
 17. Thebattery of claim 13, wherein the concentration of the carbon-basedadditive relative to the paste is approximately 0.3 to 3% by weight. 18.The battery of claim 13, wherein the concentration of the carbon-basedadditive relative to the paste is approximately 0.3 to 2% by weight. 19.The battery of claim 13, wherein the carbon-based additive has a totalpore volume of greater than about 0.2 cm³/g with a predominant pore sizeof less than 20 Å.
 20. The battery of claim 13, wherein the carbon-basedadditive has a total pore volume of greater than about 0.2 cm³/g with apredominant pore size of 20 Å-500 Å.
 21. A battery, including a negativeplate, comprising a carbon-based additive comprising graphite having asurface area of at least 3 m²/g when an amount of the carbon-basedadditive in a paste is approximately 0.3 to 6% by weight, wherein thecarbon-based additive has (i) between about 20 and 40 percentmicroporous carbon particles of the total amount of carbon-basedadditive by weight; (ii) between about 60 and 70 percent mesoporouscarbon particles of the total amount of carbon-based additive by weight;and (iii) between about 0 and 10 percent macroporous carbon particles ofthe total amount of carbon-based additive by weight.
 22. The battery ofclaim 21, wherein the battery is capable of at least 145,000 cycles in anon-stop, power-assist test.
 23. The battery of claim 21, wherein theconcentration of the carbon-based additive relative to the paste isapproximately 0.3 to 3% by weight.
 24. The battery of claim 21, whereinthe concentration of the carbon-based additive relative to the paste isapproximately 0.3 to 2% by weight.